Question: If $x@y=xy-2x$, what is the value of $(5@3)-(3@5)$?
Explanation: $5@3=5\cdot3-2\cdot5=5$ and $3@5=3\cdot5-2\cdot3=9$, so $(5@3)-(3@5)=5-9=\boxed{-4}$. Another way to solve this problem is to realize that the expression $(5@3)-(3@5)$ is of the form $(x@y)-(y@x)=xy-2x-yx+2y=-2x+2y$, so the expression is just equal to $-2\cdot5+2\cdot3=\boxed{-4}$.